Vacuum tube oscillator system



MalCh 4, 1952 M. MORRISON 2,587,750

VACUUM TUBE osoILLA'roR SYSTEM Filed Nov. 5, 1948 5 Sheets-Sheet l March4, 1952 v M. MORRISON 2,587,750

VACUUM TUBE oscILLAToR` SYSTEM Filed NOV. 5, 1948 5 Sheets-Shes?l 2 l lJl/L' A FJ l Amir/h I 1 1 l 'M L l l L l l www 4"7"- Y |r W l W PuffCamif/r' n A MIA .t0/MMM;- l l March 4, 1952 M. MORRISON VACUUM TUBEoscILLAToR SYSTEM 5 Sheets-Sheet 3 Filed Nov. 5, 1948 M. MORRISON VACUUMTUBE OSCILLATOR SYSTEM March 4, 1952 F'iled Nov. 5, 1948 5 Sheets-'Sheet4 Ey. J5

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March 4, 1952 M. MORRISON 42,587,750

VACUUM TUBE oscILLAToR SYSTEM Filed Nov. 5. 1948 5 sheets-sheet 5 o A jmw xwmw Patented Mar. 4, 1952 UNITED STATES ATENT OFFICE Claims.

The present invention relates generally to electron discharge tubeoscillators, in particular to systems of feed-back in such oscillators,and more specifically to the employment of multiple feed-back systems toa single tank circuit.

This application is a continuation in part of application Serial No.1,595, nled January 10, 1948.

Among the objects of the invention are: to provide an oscillator whichmay operate at a frequency having a degree of freedom independent of thenatural period of the controlling tank circuit; to provide an oscillatorwhich may opcrate over a wide range of frequencies with a fixed LC inthe controlling tank circuit; to provide an oscillator which may operateat the maximum degree of controlling-tank-circuit apparatus eiciency forany character of oscillator load; to provide an oscillator which mayoperate at the maximum degree of controlling-tank-circuit electricalelciency for any character of oscillator load; to provide an oscillatorwith an indirect inductive reactance stabilized feed-back; to provide anoscillator with a direct condensive reactance stabilized feed-back; toprovide multiple feed-back circuits of different reactive characters,permitting variation in oscillator frequency t performance with Xed LCin the tank control circuit; and various and other objects which will bepointed out and obvious to those skilled in the art to which theinvention appertains, upon reading the specication hereunder, inconnection with the accompanying drawings.

A The nature of the invention resides important- 1y in the employment ofoscillator structure and method of oscillator operation, which dependsupon a novel discovery in oscillator functioning, orat least in a novelcombination of underlying theories, not heretofore collectivelyconsolidated into a working explanation of oscillator operation. y

VIt; is believed that in order to give a full, clear and exactdescription of the invention, it will be necessary to provide a fuller,clearer and more exact theory of oscillator operation, as applied to thepresent invention, than is known to the applicant in published texts.The applicant will provide herein such eXtra-conventional theory as isthought to be pertinent.

The invention will be Vmore .fully understood from the followingdescription and eXtra-conventional theory, when read in connection withthe accompanying drawings, of which:

Fig. 1V is 'a diagram illustrating the. method employed by the applicant.tov determine .the

phase angle between the voltage and the current, the gure of merit Q,the resonant frequency, the frequency of the natural period or freeperiod, and the frequency under equal reactance or equal susceptanceoperation, of a tank circuit when referred to herein.

Fig. 2 shows graphs illustrating some 'of the operation of Fig. 1.

Fig. 3 shows a particular oscillator operating under condensive loadingand Figs. 4 and 5 are other oscillator circuits which are used inillustrating the' extra-conventional theory given herein;

Figs. 6, 7 and 8 are graphs relating to the oscillators shown in Figs.3, 4, and 5; and

Fig. 9 is adiagram illustrating the methods of making tests which definecertain terms used in the extra-conventional theory presented herein.

Figs. 10 and 12 are simple circuits illustrating and correcting some ofthe fragmentary theory vectorically represented in Figs. 11 and 13 ofthe prior art, not heretofore associated with oscillator operation.

Fig. 14 is a diagram of an oscillator circuit having a degree offrequency freedom independent of the LC of the tank circuit controllingthe oscillator output.

Fig. 15 is a diagram of an oscillator having a reversed inductivelyreactive stabilized feed-back, and which oscillator may operate at theresonant frequency as well as at other frequencies of the controllingtank circuit, and Fig. 16 is a vector diagram relating to the operationof Fig. 15.

Fig. 1'7 is a diagram of an oscillator having a multiple or polyphasefeed-back, one of which is reversed and one of which is direct. Undermultiple feed-back operation, this oscillator may operate at theresonant frequency, as well as at other frequencies, of controlling tankcircuit; and Fig. 18 is a vector diagram relating to the operation ofFig. 17.

Fig. 19 is a diagram of an oscillator having multiple feed-back; onefeed-back being in phase with the plate voltage and having a magnitudeproportional to the amplitude thereof, and one feed-back being in phasewith the effective alternating plate current, and having a magnitudeproportional to the amplitude thereof. Under multiple feed-back.operation this oscillator may operate at the resonant frequency, as wellas at other frequencies, ofthe controlling tank circuit, andFig. 20 is avector diagram relating to the operation of Fig. 19. y The outstandingliterature of the prior art on oscillators is replete with statementswhich indicate that the authors did not appreciate the operationaltheory as set forth by the applicant herein.

In Morecrofts book, Principles of Radio Communication, Wiley, 3rdedition, immediately after showing (beginning p. 575) that the gridvoltage of an amplifier is in phase with the tube voltage and tubecurrent only under conditions of having a pure resistance load, he, onp. 581, under the heading General analysis of conditions necessary forself-excitation (of oscillators), states; The plate potential and thegrid potential both undergo sinusoidal variations of potential in op-Vposite phases, and that the relative magnitudes of these two potentialvariations can be properly adjusted for the tubes being used.y Further,-he bears out this statement in his Fig. 146,*p. 591. This shows that hedid not consider his preceding amplifier theory to apply to oscillatoroperation.

Prince and Vogdes in their book Vacuumy Tubes as Oscillation Generators,publishedy in 1929 by General Electric Company, devote their entireChapter V to a treatment to show how the grid voltage can be made tooperate in phase (opposite) with the plate voltage (on an inductiveload) and thereby accomplishing whatv Morecroft set forth, as aboverelated', to the operation of the grid voltage in opposite phase rela,-tion tothe tube voltage. The statements made in their Chapter V showthat the authors not only believed that these phase relations could bemet (with an inductive load) but attempted to show how it could beaccomplished.

Terman in his book Radio Engineering, Mc- Graw-HilL 1937, on page 356,under the heading "67. Frequency and frequency stability ofgeneratedoscillations, states: The alternating current generated by thevacuum tube oscillator has a frequency such that the voltage which theoscillations apply to the grid of the tube is of eX- actly the properphaseto produce the oscillations that supply the required grid excitingVoltage. This approximates the resonant frequency of the tuned circuit,but This statement must4 mean that the feed-back voltage is applied tothe grid and that the resulting frequency approximates the resonantfrequency ofthe tuned circuit.

There are many other consistently expressed statements in the prior artliterature such as, that an oscillator should operate at the naturalperiod of the tuned circuit and related statements.

The applicant has discovered that:

(a) The operating frequency of' a vacuum tube oscillator bears nonecessary direct relation to the resonantr frequency of the tunedcircuit.

(b) The natural period of a tuned circuit has no physical significancein a vacuum tube oscillator operation, except as it is related bydefinition to the figure of merit Q of the circuit.

(c) The grid voltage of the tube can be in opposite phase with the tubevoltage and in phase with the tube current', only under conditions whenthe load is of an effectively resistive character. Y

(d) Under reactive loads of'any character, the grid voltage, the tubevoltage and the tube current are always all out of phase, one with theother.

(e) In oscillators, the grid voltage, the plate voltage andl the platecurrent, have the same relations as given for amplifiers by Morecroftabove, for inductive loads, but his amplifier analysis does not apply tocapacitive loads, and it is not seen how it correctly representsamplifier operation. That is, the character of the load Xes what theapplicant terms the grid operating voltage angle, which is the phaseangle at which the grid must operate under the given load. For areactive load this angle always lies in between the tube voltage and thetube current (plus or minus (f) In an oscillator operating under areactive load, any attempt to bring the phase of the grid voltage into aphase position different from its naturally assumed phase position, willcause a shift of oscillator frequency to a different frequency, whichwill cause the grid to assume a new proper out of phase position. Thephase of the grid can-not be.corrected on a reactive load to anarbitraryphase position.

(g) In a tuned grid reactively loaded oscillator, the generatedfrequency is determined by the frequency at which the grid tank circuitmust operate to produce the required grid operating voltage angle (G. O.V. A.), between the tube voltage and the grid voltage, which may belead- ,J ing or lagging depending upon the character of the load, andtherefore the oscillator frequency may be below or above the resonantfrequency of the grid tank circuit.

(h) The figure-of merit Q of the tank circuit taken at resonance is notthe operating Q of the circuit underv reactive load, because the tankcircuit does not operate at resonance under these conditions.

(i) The frequency stability ofA a resistance stabilized koscillator isnot necessarilyrcritical to the Q ofthe tank circuit, because thefrequency stability is dependent upon the G. O. V. A. being maintainedat the correct position with variation in the other circuit parameters,rather than. the circuit dissipation.

(i) The variation in the tank circuit Q with different applied tankcircuit voltages plays an important role in compensating for variationin the phase angle of the load current with different applied loadvoltages.

(lc) The grid tank circuit in addition to functioning as an electricalflywheel for the circuit performs the important function of acting as anautomatic G. O. V. A. adjuster.

(Z) In a grid tanvc circuit oscillator having an inductively reactiveplate load, inductance variations and/or variation in the Q of the loaddue to any cause whatever, and generally importantly to variations inthe applied rload Voltage, cause changes in what the applicant terms theload imposed current angle (L. I. C. A.), For each change in the L. I.C. A., there is required a correct change in the G. O. V. A., tomaintain the lsame oscillator operating frequency. Oscillator operatingfrequency stability is attained when the grid tank circuit (includinggrid current) automatically adjusts the G. O. V. A. to the correct value.for the new L. I. C. A. at the correct operating frequency.

(m) In a resistance stabilized grid tank circuit oscillator having aninductively yreactive plate load and a single` feed-back circuit, afrequency is best stabilized against plate voltage variations, when thetank circuit is operating at a frequency considerably removed from theresonant value thereof;

(n) In a resistance stabilized grid tank circuit oscillator having aninductivelyv reactive plate load, the most purely sinusoidalplatecurrentl is attained, when the tank circuit is operating at a of 10,000ohms.

frequency considerably removed` from the resonant value thereof.

Q (o) When van oscillator tank circuithas an intermittent drain imposedupon it, such as by intermittent grid current, tank vcircuitreplenishment current in phase with the intermittent drain, distorts thesinusoidal character of the tank' circuit voltage.' Therefore anoscillator should not 'be operated with thesetwo factors in phase, ifsinusoidal operation is desired.

(p) Oscillators having inductively reactive plate loads, have aninherent tendency to produce sinusoidal currents and distorted tubevoltages. (q) 'oscillators having condensively'reactive plate loads,have an inherent tendency to produce distorted 'current-sand sinusoidaltube voltages. v

(r) Oscillators having condensively reactive plate loads when operatingindependently. are more diiiicult to stabilize than oscillators havinginductively reactive pl-ate loads, but are more sensitive to injectedsynchronizing currents, than the'latter.

' The above statements'represent some important discovered facts uponwhich the present disclosure on which the illustrated embodiments of vmyinvention depend. Y

In order to establish these discovered facts, the applicant will nowtreat the extra-conventional theory required to fully understand thesestatements. n

` To makeit perfectly clear what the applicant means by the terms heuses herein, those terms which are not clearly fixed by universallyaccepted definitions or by universallyV accepted methods of experimentaldetermination, will be treated in detail.

All of the discussions herein relating to frequency are made', forsimplicity, with audio frequencies in mind, and the circuits have allbeen checked at 600 cycles or around this frequency 'as a center point.All discussions and determinations are made for operating currentorvoltage values, and are not made under artificial conditions.` Forinstance, the Q of an iron-cored coil. not only depends upon thefrequency, -but also upon the voltage applied to it, so that the Qthereof made under conditions other than operating conditions, ingeneral does not represent 'the operating Q. While some of such coilsshow a fairly constant inductance for increasing values of appliedvoltage or current, none possess a constant Q under such conditions. anexample, the inductance of a good iron-cored coil may not increase morethan 0.1 for double applied voltage, whereas the Q of this coil may'drop off` 10% under the same conditions, and a good understanding ofthis fact is essential to a clear comprehension of the disclosureherein. The method of measuring the phase angle, as

used herein, of a tank circuit is illustrated in 'Fig. l,v by closingthe switch |0|. The generator "line voltage is projected upon theoscilloscope screen, through the A input of the electronic switch, thisimage also, under the conditions ofv test, represents the tank circuitline current. The generator line voltage measurement, which is coupledto the A input of` the electronic switch, i-s made by a resistance dropmethod, but across a small percentage of the total resistance used.Referring to the gure, the total resistance of the resistor |02, may beof the order of 1,000,000 ohms, and the resistance `across the input oftransformer |03, may be of theorder Transformer |03, is preferably(Radio an extremely high-fidelity extremely small type such as go bysuch trade names as, ouncersr inchers and so forth, and should have aninput impedance of the order of 1,000,000 ohms. The fidelity and ph-aseangle vof this coupling can always be checked, by use of the electronicswitch projecting the transformer input and output voltages on theoscilloscope-screen, simultaneously. Y The form and phase position ofthe tankl circult voltage is projected superimposed upon the linevoltage image upon the screen, by means of a special A1 amplifierthrough input "B of the electronic switch. With a precisionoscilloscope; both' wave amplitudes and phase displacement can be readwith a good degree of accuracy. Y The special A1 amplifier is'constructed to have, at the frequencies employed, negligiblephasedifference between the input and output voltages, but without any'necessarily high amplification.- Such an amplifier may be constructedlike a resistancecoupled-outputy design, but with the" couplingcapacitor having arelatively large capacity, and the output resistorhaving an ohmic value relatively-very high to that of the plateresistor? Phase' difference between the input and output can be testedby an electronic switch as related abovef Y l i By varying the frequencyof the 40 polegenerator, the familiar resonance' curve, together withAthe related curve showing the phase angle between the tank-circuitvoltageV and the tank circuit-line current can be accurately determinedunder conditions representing operating voltage andv current values.Such a set of curves- -is shown in Fig 2, line C. These are the tankcir"- cuit-voltage and current values and phase relations referred toherein. J .There seems to-'be some confusion in-the literature about thedefinition-of Q-and-the method of determining it. It is usually definedas the ratio V y fi but it isl sometimes also. defined in the same texta-s the ratio volt amperes watts Engineering Handbook, ,1 -lenny,McGraw-Hill, 1941, pp.,1323) which is notthe same expression because thelatter The two expressions are only approximately lequal for'l-argevalues of Q.

For values o'f Q, where the phase angle between 'the voltage` andcurrent of the coil underv test .can be accurately determined byoscilloscopio indicationcircuit of Fig. l, is employedphy clos'- Vingswitch |0|, and opening switch "|04, The Q of the coil alone as definedby the ratio lrapidly even with ,small angular increments, that-accuracy in this range is difficult to attainqay this method. .Forthese higher values of Q the applicant measures vthe series capacityvrequired to neutralizeetbefinduetance of '.tnecoil-at' the operating-nd frequency,.by closing switch 1.0i, switches H14.; and!0.1.and.measurr.1gthe capacity-required@ condenser l06. .to produceresonancaas indicated @n the oscilloscope screen. Eromg this capacityreading the value Aof -Lis conmutedandl sdeterminedfrom the COlVOlt-71th thefvalueeof.Lknown Q iS then-.deh d for each or all values ofvoltage-,and frequency desired- I'e accuracy inaadiierence of phase.angle 4 We measured on the oscilloscope screen, which frequires axed'positionof the tracesof the were ivrms AIneasurecl .independent f ofV'the amplitiidcof the .-synchronizingvoltage, the applicant employs Athe method of synchronization .1..is =l is.f1v in latentfno. 2.435.751..

hes'applicant herein distinguishes lbetween the' veteranen of a lparallel resonance `circuit ,underonditions of resonance operation, of

natural period operation, and of'equal rgactance one 'omas Set. forthby. H.J Boyland inExper-imfntal Wireless foi-November `1927. H oweverattention -is called to the kfact that this articleffcontains formulas.having .typographical neef-"of the apparatus lshown in Fig. 1. The

method employs the use .of the synchronous con-.- ta'oto'rwhich closesthe generator supply voltage .to the L.parallel resonance circuit for aperiod of time sufficiently long to permit the .circuit .to reach al'steady `state. condition, and -then jdis- 'connects-theisupply voltageand allowsthe cir- .cuitr to oscillate at' .itsjfreej (natural) v periodlong enough to count the number of natural periods as compared to adenite number of timing Waves thrown on to the oscilloscope screensimultaneously;..by .means .of the electronic switch. This methoddetermines the natural period of the cir.-` cuit under actual conditionsof the operation.

Fig..j2, line A showsthe'appearance of the natural period beingmeasured, and line B, shows y ythe:appearance:off-the timing wave. Inpractice AlinesrA and B,- are superimposed *for convenience tor308,.across theN central position of` resistor 3.0 l When switches 306and 301 are openandswitches 3.02 yand .303 are. closed .thezdiagram willbe referred tor-as circuitC. When switches 3.06. and Q01-are closed.andswitches .302 and 3.03 areopen thed-iagram willbe referred to ascircuit D.

Fig. 4 shows a push-pull oscilla-tor 4having a resistance stabilized,feed-back and purey resistive loadingin vthe plate circuits. Theudiagram .of this gure .vwillbe ref erredto as` circuitE.

,F ig5 shows .a push-pull. oscillator having a. resistance stabilizedfeed-,.back; theplatecircuit has a split inductor. 50| .with a centertapped resistor 502. inserted. between the split coils. Y.This part ofthe diagram will be referred to as .circuit F. The figure also has .aset 1of switches 503.and 504 for introducing parallel variable capacitor505 acrossfsaidsplit inductor; withswitches503 and 504closedvthe gurevwill bereferred toas circuit G. Y

Thedetailsof Figs 6, 'land 8 will be discussed under the operation ofFigs...3, Land 5,.'butibefore these operations are taken up, it isnecessary to establishand define certain factors whichenter intosaidoperations, `andwhich are ,explained in connection with In Fig. 9, thepart of the diagram-ivhichlies entirelyfoutside ofthe dottedareas I'andJ, constitutes a circuit lidentical .with circuit IF Vof Fig. 5 .andwillbe referred toas circuit Fi,.and while other circuits may be substitutedlinits place, the illustrated circuit suliices for purposes ofillustration. `The circuitiFi of V,theflgure providedwith a set ofswitches l9D Iv and .$02, which may be thrown .to disconnect the vgrids.of ythe triodes fromthe .oscillatory system andv connect the grids to avariable frequency cententapped source ofvariable .alternating current903. YThe figure shows anddenesthree methods otmeas.- .urement ,whichwill bereierred vto hereinafter, namely:

Grid `voltage measurement, which is employed to measure .voltage valuesand phase positions.

under conditions in .which no linecurrent andl no appreciable. linede-setting is permissible. This method` is Vusedalso for obtainingthephase .angle in counting and -measuring yIf variable ire- :circuit isbelow the resonancefrequency thereof,

and the frequency at4 which equal reactance is obtained is below thefrequency of the natural period, as illustrated along line C, Fig. 2,together with formulas showing how the angles between :fthe;yoltage;.;and.=. correnti calculated, 'fior the Yfre- .quency employed.

'.Fg-jii3 .showsia :push-pull I .oscillatorv having ==a resistancestabilized: `feed-bach; the plate circuit -has saflcenterftappedYresistor y301, -one ,set "of fswtohes i302 `and 303 forlintroducingparallel '-variablecapacitors 304 land v'30'5across vthe-ends orresistor 30I,and a second set of switohesg:audaci-'1forintroducinenarallelyariablecapacibetweenthe W'Jltagev andthev ,current in A.a parallel oscillatory system, lunder similarconditions. YThe devicewithin dotted. area H `is aspecial Ai .amplierwhich is constructed to have negligible Vphase .difference between theinput .andoutput tested by means of an electronic-switch and a cathode.ray oscilloscope.

Plate vcurrent measurements (thealternating lcurrent'component thereof)are madel by what may becalled .a resistancedrop method. Re-

.ferring to Fig. 9. the .center tapped. resistorlallll is ahighly'accurate,noneinductive resistor which left permanently inthe,circuit` and has suiicient resistance to give a usable lreading onhigh-resistanceyoltmeter V. M. The lvoltmeter .resistance shollld'be of,the .order of 100 times that vof the resistor. Any direct fcurrentpresentin the resistoris prevented. from .entering the plate. .cur-.rent nieasurementircuitby capacitor-.305. The

valueof thecurrent in .the resistor is obviously determined by Ithevoltineter. For ytaking oscilloformers sold as high-delity types may nothave a zero phase difference between the input and output for thefrequency used.

Tube voltage measurements (thealternating current component thereof) aremade by a re- .sistance drop method but across a small percentage of thetotal resistance used, and if the total resistance used effects thecircuit constants, `the shunt resistance is either left inthe circuit oran equivalent resistance is substituted, so that the operation of thecircuit without the measuring device is the same as when it is in use.Referring to the circuit within the dotted area J,

the total resistance points 901 and 908 may bef of the order of1,000,000 ohms, the effective rev ,sistance across the input oftransformer 909 may be. of the order of 10,000. Transformer 909 ispreferably an extremely high-fidelity .extremely small type such as goby such trade names as ouncers, inchers and so forth, and should have aninput impedance ofthe order of 1,000,000

ohms. Y

These combinations should always be checked ,for phase difference. With100 plateA. C. volts obtained w good oscillograph defections are throughan electronic switch, with the values given. With the circuit asconnected in Fig. 9,

lthe measurements arethose of the circuit as an oscillator. Withswitches 90| and 902 thrown to Vconnect independent A. C. source 903,the meas,- furements are made on an amplifier and obviously phase anglemeasurements can be made on various parts of the circuit at any desiredfrequency. A Certain experimental facts which the applicant hasdiscovered will be established on the operation of Figs. 3, 'l and 5,based upon measurements taken by the circuits explained in Fig. 9.

Referring to Fig. 4, if the voltage values and.;-

phase angle are taken of the parallel oscillatory circuit alone ofcircuit E, as a function of the applied frequency at a constanteffective current, there is obtained the familiar resonance-voltagecurve 10| and its phase angle curve 102, with reference to said current.If said oscillatory circuit is tuned to resonance at say X cyclesindependently and then put into circuit E, and the feed-back resistorproperly adjusted, circuit E can be made to oscillate at X cycles or theresonant frequency of said oscillatory circuit.

However if the same oscillatory circuit with its X cycle resonant tuningand with the same adjustment of feed-back resistors, is substituted incircuit F and the proper measurements made,

it will be found that circuit F does not oscillate at X cycles, but atsome higher frequency 80|, Fig. 8, and with a lower output with the sameplate impedance, because it will be found that the grid voltage islower.

Then ifrswitches 503 and 504 are closed with ,low capacity adjustmentofV capacitor 505, it will be found .that by increasing said capacitythe frequency and grid voltage can be brought to the values of circuitE. Further adjustments Vof said capacity will lower the grid voltage.

Now if the same oscillatory circuit with its X Y cycle resonant tuningand with the same adjustment of feed-back resistors is substituted ineither circuit AC or D, say in'circuit I3. it will be 10 found thatcircuit D does not oscillate at X cycles, but at some lower frequency60|, Fig. 6, and with a lower output with the same plate impedance,because it'will be found that the grid voltage is lower.

It willbe found that other factors, like amount of feed-back resistance,Q of oscillatory circuit at the frequency and voltage employed, andother factors which are beyond the scope essential to this disclosure,also affect the oscillator frequency.

From the above tests it has been discovered that the circuits C, D, E, Fand G, can be made to oscillate at the same frequency by employingdifferent LC values in the parallel oscillatory circuits.

If the parallel oscillatory circuit of circuit F is set so that circuitF oscillates at any 600 cycles, it will be found that the oscillatorycircuit voltage values and their 'phase relation to the tube voltage(oscillatory circuit current) as a function of the circuit frequency, isrepresented by Fig. 8, in which the frequency corresponding to the line80|, represents 600 cycles. Assume the phase lead shown to be say 60,which is a practical value. This means that the grid voltage lags thetube voltage by 60 and that the oscillatory circuit is not operating atthe resonant point, but in the steep region of the high-frequency sideof the resonance curve.

By increasing the inductance of coil that is by increasing the phaseangle between the A. C. tube current and the A. C. tube voltage, theline 80| moves to thevright and the operating frequency is increased,and by *decreasing vthe inductance of coil 50|, the operating frequencyis decreased. A

As it has been indicated, circuits C, D and G, can be adjusted so thatthe grid voltage leads the A. C. tube voltage at the operating frequencyand say this frequency is 600 cycles and is represented by line Fig. 6.Obviously increasing the shunt capacity of these circuits, decreases thefrequency thereof and decreasing the capacity increases the frequency,Within proper operating limits.

With these experimental phenomena disclosed, the applicant willestablish a working theory for the making of oscillators in accordancewith his invention, by the application of the analysis of amplifieroperation.

In dealing with oscillators having an inductive load, use will be madeof Morecrofts analysis of inductively loaded plate circuit amplifiers(in his. above-referred to book, page 575), but the analysis given byhim for capacitively loaded amplifiers is discarded, because it cannotbe validly applied, as willbe more fully pointed ou hereinafter. Y Y`While the Morecroft analysis used herein is not a mathematically exacttheory, even for amplifiers, it does provide a practical Working theory,at least for audio frequencies, for the employment of the presentinvention, in the making of oscillators having inductive plate load.

A mathematically exacttheory.ofoscillators made in accordance with theteachings of the present invention, as determined by settingl updifferential equations forthe operation of the tube with its connectedcircuits, -and obtaining solutions for them -for a particular set ofconditions, by numerical methods, leads to difficulties. which prevent.such solutions from helpfulgin the making of oscillators.. a,However-the.deferment ,of the .there .being given herein, issuliciently accurate to enable one skilled in the art, to make anduse-oscillators` employing circuit elements having individually fixedcircuit parameters, whichelements when properly combined intooscillatorecircuits, result'in oscillator operation ata predeterminedfrequency without circuit tuning, which is broadly new, to the bestknowledge obtained by the applicant.

Referring to Fig. l0, this lwill beY recognized by those skilled in theart, as a circuit which may be operated either asV an amplifier or as anoscillator depending upo-n whether the switch 00! is closed upon contacti002 or upon |003. Switch |001 -is rst closed upon contact `0132 andamplifier operation is obtained from alterna-ting voltage source i004,and the resulting circuit is taken tooperate in accordance with theassumed theory and analysis of Morecroft.

Fig. 11 is taken substantially from the Morecroft book and representstheapproximate analysis, of the above circuit on'the assumptions made byhim in arriving at his analysis. The vector notations are conventionaland will be understood by those skilled in the art. For the basicassumptions andy development of the theory, those skilled in the art arereferred to the book. It isl to be noted that the voltages and currentstreated, are the alternating lcomponents of the voltages only.

In the operation of amplifiers, it is to be noted that with inductiveplate load, the grid voltage Eg, does not and cannot b-emade to operatein phase with the tube voltage or in phase with the plate current. Thegrid voltage Eg (reversed in phase) must and does always lie,4A in phaserelatiom between the tubevoltageEp'and tube current lp. This is setforthasV amplifier operation only and nowhere in the prior lart Idoes theapplicant nd this analysis developed for oscillator theory and further,all oscillator theory which has come to the attention of the applicant,is inconsistent with this analysis when applied to oscillator theory andin some cases entirely contrary thereto.

If the amplifier of Fig. 10 resulting from closing switch |001 uponContact |002, operates in accordance with Fig. 11, by changingthe'source of grid voltage will not change the Vnecessary phase relationestablished between the, tube voltage Ep, the grid voltage Eg andthe,plate current lp. Therefore ifswitch ll, is closed upon contact i003;forming an oscillator ofthe circuits of Fig. these saidphase relationsmust be maintained if the oscillator frequency is to be thesame'asthat'under amplifier operation.

Since thephase relation between the grid voltage Eg and the tube voltageEp, must remain as shown in Fig. 1l, the tank circuit I005'of iFig. 10,must supply this difference ofphase position of these two voltages. Inthe figure, the tank circuit current has the phase position of the tubevoltage Epand the tank circuit voltage mustlag the tank circuit current,by the exact value which provides the grid voltage Eg, `as called for inFig.

Cil

l2 cillate at a frequency higher thanV the-resonant frequency of thetank circuit, as described as an experimental result in connection withFigs. 5 and 8.

It is entirely impractical as well asimpossible to develop, in a patentapplication specification. this theory and analysis for all types ofoscillator circuits, and all the discussion herein is directed to thetypes of circuits shown in Figs. 3, 4, and 5. It is believed thatdisclosing a good teaching of the theory applied to these types ofcircuits, will provide those skilled in the art Vwith su'icientknowledgeof the subject to enable them to apply and embody theprinciples in other types of circuits.

It is obvious, to those skilled in the art, that under the aboveteaching the grid voltage phase angle cannot be corrected to any angledifferent from the G. O. V. A. which is determined by the L. I. C. A.,without changing the frequency of oscillations, and further underinductive plate loading, the G. O. V. A. cannot be brought into phasewith the tube voltage or tube current under any conditions of operation.

Also the natural period of the tank circuit is not directly involved inthe frequency of operation of such an oscillator, since the naturalperiod is the period at which the tank circuit operates when freej thatis when itis not being driven, whereas in oscillator operation the tankcircuit is driven at the period which provides the necessary G. O. V.A., and there is no necessary direct relation between the two periods.The Q of a tank circuit influences the free period thereof `as aseparated consideration, whereas the Q of a tank circuitas it functionsin an operative element in an oscillator inuences the difference betweenthe free period and the driven .period ,of the tank circuit of such anoscillator.

Referring to Figs. 5 and 8, the higher theQ of the tank circuit, theclcser will be the operating frequency to the resonant frequency of thetank circuit. However good stable operation can be obtained with anoperating Q (Q of tank circuit takenunder operating conditions) as lowas 5, and probably lower. Operating Q is not to be confused with'Q takenat resonance frequency of the tank circuit, as this condition oftenindicates a higher value. The operating Q of the tank circuit in Fig.10, must also includethe grid losses.

Attention is directed to the factthat in anoscillator, having aninductive plate load. the-tube reaction is in series .with the loadinductance and therefore the load inductance functionscharacteristically toi reduce harmonics in the tube circuit current, anyharmonics present appearing inv the voltage. This accounts for thefactthat such oscillators usually producea tube current having a good sinewave-form, and a tube voltage having a considerable harmonic content inthe vwave-form thereof, mostly even harmonics introduced by the tubecharacteristics. It is to be borne in mind that-in any circuit havingthe property of producing harmonics,Y` they -canhbe reduced orleliminated in the currentl or in 4the voltage of the circuit, but notin both. The inductively loaded oscillator reduces them inthe current,and their reduction in capacitively load oscillators will be treatedlater on herein.

Now concerning this disclosed oscillator theory as applied tocapacitively loaded oscillators. the amplifier analysis as ,given byMorecroft above, cannot 4be validly applied, because his analysis.

V13 as applied to amplifiers, as understood by the applicant isincomplete, faulty and incorrect.

Morecroft does not illustrate the amplifier circuit from which hisoscillograms of an amplifier having a capacitive load were taken. Hisvector diagram of his capacitively loaded amplifier, is a diagram of aload circuit having only a resistance in series with a capacitance,corresponding with his vector diagram of his inductively loadedamplifier circuit, in which he does have only resistance in series withinductance. But the plate circuit of an amplifier (and of an oscillatoras well) is a direct current circuit as well as an alternating current,and circuits having,V

fler operation having a capacitive load and zero resistance could nothave been made with the two circuit elements in series.

The applicant discloses hereunder an amplifier circuit having acapacitive load, and a correct vector diagram therefor and how theanalysis of these may be'applied to oscillator operation.

Fig. 12 illustrates aV circuit which like that of Fig. 10, may operateas an amplier by closing switch |20| upon contact |202, or operate as anoscillator by closing switch |20| upon contact |203. The plate circuitof Fig. l2, possesses di- "rect current conductivity and capacitiveloading,-

in the resistance branch and the current in the capacitance branch, ofthe parallel load of the' tube. When dealing only with the alternatingcurrent components of the currents and voltages as heretofore premisedherein, the same is tre for the alternating current components thereon'Referring to Fig. l2, switch |20| is closed upon f contact |202, and thecircuit operates as an amplifier from a grid voltage source |204.Referring to Fig. 13, the angle of the load reactioniis seen to be thereciprocal of the value for the series circuit, given by Morecroftabove, and the z.

angles between the grid voltage and tube voltage and tube current arevery different values from those given by him for capacitive loads .(seehis page 579). A

Referring to Fig. 12, the switch |20|, is closed upon contact |203,under which condition theresultant circuit operates as an oscillatorandthe tank circuit |205, provides the G. O. V. Auasfjdetermined by thevector diagram of Fig. 13. g

The corresponding circuits of Fig. 3 operate similarly and anillustrative graph of the G. O. V. A. with the corresponding tubevoltage angles are shown in Fig. 6. Yj

Referring to'Fig. l2, it will be seen, thatuthe tank circuit current hasthe phase of the tube voltage Ep, andreferring to Fig. 13, that thetankcircuit voltage must l'eadthe tank circuit crrent to provide the G.' O.V. A., necessary for oscillator operation. This explains theexperimentally discovered operation of Fig.` 3, as illustrated in thegraph of Fig. 6, in that the oscillator operates at a frequency lowerthan'the resonant frequency of the tank circuit.

It will be seen in ,capacitively loaded oscillators that the tubereaction is partly in series withlthe ytube characteristics.

14 load condenser and therefore the load condenser functionscharacteristically to induce harmonics inthe tube circuit to appear inthe tubel current, and therefore reduce them in the tube voltage. Thisaccounts for the fact that such oscillators usually produce a tubevoltage having a good sine wave-form, and a tube current havingconsider'able harmonic content in the wave-form thereof, mostly evenharmonics introduced by the If the oscillator of Fig. l2 has switch |206opened, all the angles of the diagram of Fig. 13 disappear and allvoltages and current are thrown into phase. This explains the operationof the oscillator of Fig. 4, as experimentally determined by the graphsshown in Fig. '7.

With the experimental disclosures and explanatory operating theorydeveloped above, and with the aid of the measurement directions givenherein, the applicant now shows how his discoveries can be embodied insome other new and useful devices. l

Fig. 14 shows an oscillator in which the tank circuit has a fixed LC,and it is caused to operate over a wide range of different frequencies,by in'- terposing, in the oscillator feed-back circuit, a feed-backphase shifting means.

The circuit enclosed within the dotted area J, is an oscillator of the Ftype shown in Fig. 5, when switches 40| and |402 are closed respectivelyupon contacts |403 and |404. As a specific` example, switches |40| and|402 are closed, the tank circuit |405 and the feed-back resistors areadjusted to give stable operation at 600 cycles. The G. O. V. A. isdetermined by the method illustrated in Fig. 9. This oscillatorwith thesame feed-back current and the same G. O. V. A. will oscillate at 600cycles regardless of the source of the feed-back current. Also thisoscillator operates at other frequencies for other phase positions ofthe G. O. V. A. as shown experimentally in Fig. 8 and analytically inFig. 1l, so that interposing a phase shifting in the feed-back circuitof the oscillator enclosed within the dotted area J, will result in anadjustable frequency oscillator having a fixed LC in the tank circuit.

Referring back to Fig. 14, the circuit enclosed withinthe dotted area K,is an amplifier having a resistance-capacitance output and a phaseshifting means in the input circuit; In'the form illustrated this phaseshifting device is a parallel inductance-capacitance circuit having anadjustable LC, but any other suitable phase shifting means may be used.j

Switches |40| and |402, are opened and switches |409 and |4|0 are closedrespectively upon contacts |4|| and |4|2. The condenser I4| 3 isselected so that at its middle point, the phase angle of the output ofthe amplifier is eX- actly in phase with the oscillator tube voltage,then the'feed-back angle to the oscillator tank circuit through theamplifier, is the same as when switches |40| and |402 were closed, hencethe oscillator operates at 600 cycles, as it did originally. Adjustmentof 'condenser |4|3, causes the oscillator to run faster or slower,depending upon whether the G. O, V. A. is increased or decreased,r asillustrated in Fig. 8. f

vIt has been stated (F. lTermanjResistance stabilized oscillators,Electronics, July 1933) that in oscillators which he describes, whichare type Vthis type can be constructed with more inductanoe thanresistance nin the .feed-back circuit, :and .op-

v-erate with 'lgood stability.

Fig. l shows an oscillator embodying the vap- `plicants discovery andlinvention which'has a large inductance in the feed-back circuit. The`oscillator is constructed ifor 600 cycle operation as follows:

' vFirst the circuit has the .feed-back circuit open fand the Vvtankcircuit removed. The G. O. V. A. for the L. I. C. A. determined by themethod Ishown in Fig. 9. The tank circuit is separately adjusted tokresonance by the method shown in Fig. .1. The tank circuit is thenproperly connected in the 4grid circuit as shown in Fig., 15.

The amount of feed-back current is calculated from the tubes and circuitemployed, then the inductanoe of `reactors |502 `and |503, and theresistance of resistors Y|504 and |505,1are cal- A`culated from vthewell known` vector Lrelation shown'in Fig. 16, to provide the correct G.O. V. A. vand when the feed-back .circuit is connected up as shown, theoscillator operates .at 600 cycles.

.or`very close thereto, depending upon the accuracy of vthe workperformed. Thus is produced aninductively loaded oscillator, with a tankcur- ...rent 'operating at resonance, and Withglargely inductiveimpedances inthe feed-back circuit.

When properly constructed, the oscillator shows good frequencystability.

With the teaching given in connection with Fig. further disclosure canbe made with reference to Fig. 14. `In the disclosure given for theconstruction of oscillators in accordance with Fig. 14,.directions weregiven to set the tank circuit |405, for proper noperation at the givenfrequency Withifeed-.backresistors |406 and |401 incircuit. AttentionWasdirected to the fact that the circuit enclosed within dotted varea K,constitutes aphase shifting circuit replacing these feed-back resistors.under conditions of .adjustable frequency operation.

With reference to Fig. r15, it was shown that .the Ytank circuit |50|can be set to resonance `at the frequency vof operation, when thefeedback circuit has a proper phase shifting means inserted into it.Since circuit enclosedin dotted .area K isa vphase shifting means, thetank circuit |405 of Fig. 14 can be set also to the resonance at thefrequency of operation, and the proper phase shift `of the feed-backcircuit can -be obtained by adjustment .of condenser 4'|3, ,or ofthe LCofthe circuit including ,condenser |413. Further, since .it isseen thatthe G. vO.'V. A. vrequired for any L. I. C. A. is a `Vvector result ofthe phase .angle of the tank circuit |405,v and of the .relative phaseangle of the feed-back circuit, the LC of the tank circuit |405 can havea [wide Vrangeof/different valuesfor the same oscillator operatingfrequency, ifmeansgisemployed V1in the feed-back-circuit to cause'th'eproper phase angle .feed-back current to the tank circuit for theoperating frequency desired.

.The applicant will now. give direction`s 'for the embodiment of hisdiscovery and invention in oscillators bythe employement ofpolyphasefeedlback circuits. Referring toiFigl'l, ,there is shown lfeed-backcircuitcomprising condensers |102 .and

|103, in series with resistors |104 and |105. This --circuit suppliesfeed-backlcurrent in phase with alle mure. inthe .circuit .L1-n n.. :isto were at resonance, 'the 'etank circuit 1f eedback :current must :bein phase `with the G. O. V. A. .This .is

'-Iaccomplished' in -this embodiment ,by a .direct feed-back circuit,comprising, in Fig. 17, resistors.

feed-.backlcurrent and the proper G. O. V. A. to lcause the desiredfrequency of operation of the oscillator.

' While `only two phases 4 of feed-back .current :is shown, it will .beappreciated by -those skilled in the art `of polyphase currents, thatany number `of properly chosen :phases V.may be vemployed to produce asingle phasecurrent of .a desired phase .relation to the .referencephase of thecircuit In view .of the foregoing disclosures, Vit will `beseen that the LC of the tank circuit |1.0|, .does not have to be set to,the resonant operating frequency Aof the oscillator, but may .be set atdifferent other LC values for the same operating frequency of theoscillator, if the polyphase feedback `circuits are adjusted .to providethe required G. O. V. A.,for the load employed at .the frequency vofoperation.

A further methodand structure, forsupplying polyphase feed-back.circuits to the tank circuit .as compared to the totalI load voltage,andthe secondary there of is generally shunted by a condenser |906, and.has the feed-back Aresistors |901 and |908, asa load therefor. Thiscurrent ,transformer is constructed and vadjusted such that thefeed-back load current is n'phase with, but not Ynecessarily so,.` thealternating current component of the plate load current. The phaselposition of this second ,phase of feed-back curvrrent yis identied inthe vector vdiagram of Fig.

20, and its vector composition to give the required G. O. V. A., for.thedesired operation is conventionally analyzed in theFig 20.

It will be appreciated by those skilledr'in the ,f art that, in general,the operation of the tank circuit at its resonance frequency, provides amore Y.economical use ofthefLC of that circuit and and thisisanimportant item'snce the tank circuit usually constituted anvexpensive element in the cost of oscillators.

All of the circuits disclosed herein vhave .been actually constructedvand operated as described herein at 60,0 cycles as afrequency centerpoint and thereforeany differences of opinion vas to alternateexplanations of ,the operation .does not effect .the validityl of vthedisclosures.

f .Haiing n taught herein,- the nature of vmy .dis-

Acovery andinvention, other andv further embodiments will be obvioustofthose skilled in the art.

What I 4claim is:V 1. In-.an electrical oscillation system including anelectron discharge tubehaving a plate, a Acontrolgrid anda-cathode;QalOadcircuit, ei-discharge control .circuit .including gsaid-gridf-saidlcathode l? and a tank circuit, and a feed-back circuit fromsaid load circuit to said tank circuit including electrical-circuitphase-shifting means varying the operating frequency of said system.

2. In an electrical oscillation system including an electron dischargetube having a plate, a control grid and a cathode; a load circuitincluding a reactive member, a cathode-grid circuit including a tankcircuit set to an operating voltagecurrent phase-difference having anangular value different from the grid operating voltage angle requiredfor the load imposed current angle of said system, and a feed-backcircuit from said load circuit to said tank circuit including phaseshifting circuit means compensating for said different Value.

3. In an electrical oscillation system including an electron dischargetube having a plate, a control grid and a cathode; a load circuit, acathodegrid circuit including a tank circuit, and a feedback circuitfrom said load circuit to said tank circuit including electronic-tubephase-shifting means varying the operating frequency of said system byangular variation of the grid operating voltage angle.

4. In an electrical oscillation system including an electron dischargetube having a plate, a control grid and a cathode; a load circuit, acathodegrid circuit including a tank circuit, and a feedback circuitfrom said load circuit to said tank circuit including an electronic tubeamplier having a variable LC tank circuit in the cathodegrid circuitthereof.

18 5. In an electrical oscillation system including an electrondischarge tube having a plate, av control grid and a cathode; a loadcircuit including an inductive reactor, a cathode-grid circuit includinga tank circuit set to resonance at the operating frequency of saidsystem, and a feed-back circuit from said load circuit to said tankcircuit including phase shifting circuit means causing current fed tosaid tank circuit to ow at a phase angle equal to the grid operatingvoltage angle required for said operating frequency of said system.

MONTFORD MORRISON.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date Re.21,807 Lindenblad May 20, 19412,076,264 Chireix et al Apr. 6, 1937 2,162,470 Kautter June 13, 19392,346,331 Roberts Apr. 11, 1944 2,389,025 Campbell Nov. 13, 19452,415,868 Clark Feb. 18, 1947 2,421,725 Stewart June 3. 1947 2,445,811Varian July 27, 1948 2,482,766 Hansen et al. Sept. 27, 1949 2,506,329Ames, Jr May 2, 1950

